The present invention relates to a tube connecting structure that connects a first tube and a second tube with a connecting member and uses a sealing member to form a fluid-tight seal between an end of the first tube and an end of the second tube.
U.S. Pat. No. 6,481,759 presents an example of a conventional tube connecting structure (see FIG. 17). In this tube connecting structure, a main bushing unit 3a of press-in bushing means 3 is pressed into a resin tube 1. The resin tube 1 has a flared end 1a having a large diameter. A joining member 2 is fitted to the outer perimeter of a shoulder 1b of the resin tube 1. Also, a ring-shaped sealing member 4 is mounted in a ring-shaped groove formed by: the outer surface of the flared end 1a of the resin tube 1; a ring-shaped stopper surface means 3b of the press-in bushing means 3; and a cylindrical base section 2a of the joining member 2. An insertion end 5a of a tube-shaped opposing member 5 is relatively fitted to the outer perimeter surfaces of stopper surface means 3b of press-in bushing means 3 and the base section 2a of the joining member 2. A second engagement section 5b engages with a first engagement section 2b of the joining member 2. As a result, the sealing member 4 provides a fluid-tight seal between the insertion end 5a and the flared end 1a. 
However, in this conventional tube connecting structure, a chuck tool must be used to compress the tube while pressing the press-in bushing means into the resin tube. At the same time, the chuck tool must avoid contact with the joining member. The position of the joining member must therefore be moved inward along the axis of the resin tube to allow sufficient room for the chuck tool. Consequently, the flared end of the resin tube requires a straight section having a length that includes both the length of the joining member and the length of the chuck tool. When a flexible accordion tube is to be used with this conventional tube connecting structure, a very long straight section is needed at the end of the resin tube. In this situation, installation of a tube connecting structure with an accordion tube in a small space (e.g., in an automobile) can be extremely difficult due to space restrictions because this tube connecting structure requires a long, non-deformable straight section. Also, in the case of this conventional tube connecting structure, the press-in member is prevented from slipping out due to tension on the resin tube. If the tension on the resin tube decreases, however, the press-in member can slip out, allowing the opposing member and sealing member to slip out as well. Thus, the sealing properties of the tube connecting structure can be compromised.